Such watches are well known to those skilled in the art. One of them is disclosed in Swiss Patent No. 184 338. It includes three hands each moving opposite a graduated circular dial. The hands and the dials are concentric. The first dial bears a scale each division of which corresponds to 1° of arc, placed opposite a hand completing one revolution in 40 minutes. The second dial bears a graduation of 36 divisions each of which corresponds to 10° of arc placed opposite a hand completing one revolution in 24 hours. The third dial bears a graduation of 60 divisions each corresponding to a minute of arc placed opposite a hand completing one revolution in four minutes of time. The watch further includes a ring for modifying the position of the dials in order to allow adjustment relative to the equation of time. The watch was, for example, intended for aviators to let them know their position. It permits precise determination of longitude, but is not convenient for reading the time. It must in fact remain adjusted to the time of the place of departure. Moreover, the hands rotate at an unusual angular speed.
French Patent No. 852 214 relates to a watch including two discs displaying the hour and the minute.
A third disc, which is concentric, allows longitude to be determined, insofar as the true time of the place considered is known.
German Patent No. 25 104 84 and U.S. Pat. No. 2,560,618 disclose devices for determining a location longitude and latitude. These devices cannot be associated with a watch.
Finally, French Patent No. 460 311 discloses an astronomical instrument allowing one to take bearings, track a star, etc.
Today, the GPS system allows the position of a location to be defined with much greater precision than that achieved with a conventional timepiece. People who have to know their position with precision can thus use this system without any problem. However, no means exist which are simple to use and allow explanation and understanding of what longitude is and how it can be determined with reference to time, and to the movement of the sun relative to the earth. In order to assure these functions, it is necessary to be able to use a commonly used object, involving simple and easily comprehensible manipulations which is easy to read.